I've seen that others are having this issue when trying to run Phalcon via Apache, and the suggested solution was to make sure phalcon.so was loaded after the PDO functions. I've done that as you can see here:

I should mention that I'm not having this problem when trying to use Phalcon on the web - just in the CLI application. Calling phpinfo() from the CLI application shows that Phalcon is loaded, and all the proper .ini files have been loaded as well

I tried for 1/2 an hour to fix this before I posted. 3 minutes after posting, I found the solution - I had extension=phalcon.so in my main php.ini file, in addition to being in the separate 30-phalcon.ini file. That caused the Phalcon extension to be loaded too soon. Removing the line from the main php.ini file fixed the problem